1. Field of the Invention
The present invention relates to a piezoelectric vibrating piece and a piezoelectric vibrator having the same.
2. Description of Related Art
For example, in a cellular phone and portable information terminal apparatuses, a piezoelectric vibrator using crystal and so on is used in many cases as devices used for a time source, a timing source of a control signal and so on, a reference signal source and so on. As a piezoelectric vibrator of this kind, there is known one in which a piezoelectric vibrating piece is hermetically sealed in a package where a cavity is formed.
A so-called center-arm type piezoelectric vibrating piece is known as a piezoelectric vibrating piece (for example, refer to JP-A-2003-163568 (Patent Document 1) and JP-A-2006-345517 (Patent Document 2)). The center-arm type piezoelectric vibrating piece has a pair of vibrating arm portions arranged in parallel to each other at an interval in a width direction, a base portion supporting a base-end portion side of the pair of vibrating arm portions in a cantilever manner and a support arm portion (center arm) extended from the base portion between the pair of vibrating arm portions. Then, the piezoelectric vibrating piece is mounted inside a package by using the support arm portion as a mount portion. Specifically, two mount electrodes provided on the surface of the support arm portion are bonded to electrode pads on a package side through a conductive bonding material such as a conductive adhesive or metal bumps. Accordingly, the piezoelectric vibrating piece can be mounted in the package as well as a voltage can be applied from outside to excitation electrodes on the vibrating arm portions.
In the piezoelectric vibrating piece of this kind, two mount electrodes provided on one surface (mount surface) in a thickness direction of the support arm portion and two-system excitation electrodes provided on respective vibrating arm portions are respectively connected through two-system layout electrodes formed via the base portion. The respective mount electrodes are arranged at an interval in a longitudinal direction of the support arm portion for securing respective insulation properties of the two mount electrodes. Therefore, the layout electrodes connected to the mount electrode positioned on a tip side of the support arm portion pass near the mount electrode positioned on the base end side of the support arm portion on the surface of the support arm portion.
According to the above, the conductive bonding material used for bonding the mount electrodes positioned on the base end side of the support arm portion is squeezed and wet-spread at the time of mounting the piezoelectric vibrating piece onto the package, which causes a risk of short circuit in the layout electrodes connected to the mount electrode positioned on the tip side of the support arm portion. The risk is increased particularly when the width dimension of the support arm portion is reduced for satisfying the requirement for miniaturization of the piezoelectric vibrating piece.
In this respect, the layout electrodes of two mount electrodes are respectively formed on side end surfaces which face each other in a width direction of the support arm portion in the piezoelectric vibrating piece described in Patent Document 2, therefore, the risk may be reduced to some degree.
However, even when the layout electrodes of two mount electrodes are respectively formed on side end surfaces which face each other in the width direction of the support arm portion as in the piezoelectric vibrating piece described in Patent Document 2, there is a possibility that the conductive bonding material on the mount electrodes is squeezed and wet-spread at the time of mounting the piezoelectric vibrating piece onto the package to reach the side end surfaces in the width direction of the support arm portions. In such case, there still exists the risk of short circuit in the layout electrodes connected to the mount electrode positioned on the tip side of the support arm portion due to the conductive bonding material for bonding the mount electrode positioned on the base end side of the support arm portion.